The established causal relationship of tabacco usage and several types of cancer and the continuation of cigarette smoking by 54 million Americans mandate that the studies on the mechanisms underlying tobacco carcinogenesis be continued and that the biological properties of new smoking products be monitored. The identification of compounds and processes involved in tobacco carcinogenesis contributes directly to the understanding of chemical and environmental carcinogenesis per se. The proposed program will elucidate the formation and mechanism of action of organ-specific tobacco carcinogens, such as the N'-nitrosamines which derive from alkaloids and from certain agricultural formulations used on tobacco crops. It will also identify tobacco-specific nitrosamines and their role in oral cancer of tabacco chewers and snuff users by chemical analytical studies and by bioassays in Syrian golden hamsters. The program will also include chemical identification of mutagenic nitropolynuclear aromatic hydrocarbons in cigarette smoke and assessment of their potential as carcinogens in small rodents. Identification of the active cocarcinogenic components of the neutral and weakly acidic subfractions of tobacco smoke condensate will focus on chemical classification and on determination of their relative activity in a newly developed short-term screening test on mouse skin epithelium. Mutagenic flavor compounds in the smoke of low yield cigarettes will be assessed chemically, as well as biologically. Bioassays will be initiated to study the effects of the major nicotine metabolites on bladder cancer induction in rats.